1. Field of the Invention
The invention relates generally to network interconnection devices, and in particular, to devices that provide interconnection between an Asynchronous Transfer Mode (ATM) network and nodes of a Local Area Network (LAN).
2. Background Information
Personal computers (PCs), servers, printers, and other such devices (sometimes referred to as xe2x80x9cnodesxe2x80x9d) are commonly connected together as a network or LAN. LANs typically operate according to Ethernet standards and protocols. With Ethernet technology, all nodes in the LAN share the bandwidth of the communication medium (e.g., twisted pair or coaxial cables) that connects the nodes together. All nodes in the LAN are reached anytime there is a single transmission of data in the form of xe2x80x9cEthernetxe2x80x9d frames having source and destination addresses. The node having the destination addresses processes the received transmission. Ethernet networks are known as xe2x80x9cconnectionlessxe2x80x9d networks because by using source and destination addresses, communication can occur without the need to first establish a connection and without immediate acknowledgement of receipt.
PCs and other devices are connected to the LAN by various Ethernet hardware interfaces installed in or coupled to these devices. For example, many PCs are equipped with Network Interface Cards (NIC), such as the commonly used Ethernet NIC card and various Ethernet controller units. An Ethernet LAN often uses carrier sense multiple access with collision detection (CSMA/CD) methods, where different nodes listen for transmissions in progress in the communication medium before beginning to transmit. However, CSMA/CD methods sometimes cannot limit the maximum access time to the communication medium, which can result in the denial or delay of access to the communication medium to one or more nodes.
While response time is sufficient for many applications, the increasing presence of multimedia video and audio has increased the need for networks that can provide guaranteed access time. Ethernet systems that attempt to handle this type of data often get bottlenecked. Therefore, it has been proposed to connect LANs to ATM networks that operate at 155 Mbps and higher. ATM networks further provide a rich environment having numerous types of traffic classes and the ability to multiplex many data streams with different handling requirements. The key feature of an ATM networks is that data is segmented into fixed lengths of data called xe2x80x9ccells.xe2x80x9d ATM networks are known as xe2x80x9cconnection oriented transmissionxe2x80x9d networks because rather than using source and destination addresses, connection is established by signaling. A connection to a remote-end station is signaled/requested, and upon connection set-up, virtual circuit identifier (VCI) and virtual path identifier (VPI) is provided to headers of the ATM cells that are transmitted.
While it may be advantageous for LANs to connect to ATM networks because of the attractive features provided by ATM networks, doing so is often impractical because of the high costs of ATM interfaces required to connect LANs and/or individual PCs to ATM networks. Also, while it may be possible to build ATM interfaces and switches having lower speeds that can accommodate Ethernet speeds, such a solution is costly because it would require replacement of existing Ethernet physical interfaces currently in use by or installed in many LANs and their nodes. Such high costs are difficult to justify for common PCs and workstations. Accordingly, there is a need to be able to connect nodes, such as PCs equipped with Ethernet NICs, to ATM networks without having to replace existing hardware interfaces.
One aspect of the invention provides an apparatus that includes a first buffer having an input that can be coupled to a network interface of a first type, with the network interface of the first type operating at a first data rate. An output of the first buffer can be coupled to a network interface of a second type that operates at a second data rate faster than the first data rate. A separation unit is coupled to the first buffer, and a second buffer has an output that can be coupled to the network interface of the first type and an input that can be coupled to the network interface of the second type. The second buffer is sized larger than the first buffer. The first buffer holds at least a portion of a first frame received from the network interface of the first type and the separation unit sends the portion of the first frame to the network interface of the second type at a data rate corresponding to the second data rate. The second buffer holds a second frame received from the network interface of the second type and sends the second frame to the network interface of the first type at a data rate corresponding to the first data rate.